SPONTANEOUS LIFETIME AND QUANTUM EFFICIENCY IN LIGHT-EMITTING-DIODES AFFECTED BY A CLOSE METAL MIRROR

The spontaneous lifetime and quantum efficiencies of dipoles placed cl ose to a metal mirror are calculated. The importance of these effects are demonstrated in the recent experimental work on InGaAs-GaAs quantu m well light emitting diodes in which the modulations rates were varie d from 0.8 GHz to 1.4 GHz through the placement of quantum well next t o a Ag mirror [Deppe et al., Electron. Lett. 26, 1665, 1990]. Classica l energy transfer theory is used to treat the spontaneous radiation of a quantum well in a semiconductor system. The spontaneous radiative l ifetime and internal quantum efficiency are strongly affected by the l ocation of the quantum well, which confines the dipoles, by the orient ation of the dipole in the well, by the metal reflector material, and by the metal mirror thickness. In general, the internal quantum effici ency decreases when the dipole is closer to the metal, because of the nonradiative energy transfer from the dipole to the absorptive metal a s discussed by Kuhn [J. Chem. Phys., 53, 101, 1970]. The overall effec t of closely spaced metal mirrors on the measurable external quantum e fficiency is presented, which is important for fast light emitting dio de design.